1. Field of the Invention
The present invention relates to a fuel-cell power generation system comprising a fuel-cell power generator adapted to generate electricity to be supplied to various electrical appliances. The present invention also relates to a control method for such a fuel-cell power generation system.
2. Description of the Related Art
There has heretofore been known a fuel-cell power generator designed to operate fuel cells to generate electricity using fuel gas so as to supply electric power and hot water. In view of power generation efficiency, it is desired to operate the fuel cells to generate electricity equal to that to be consumed by electrical household appliances. Thus, it is requited to monitor or measure the power consumption of the appliances and control the power generation or output power of the fuel cells in response to the measured value. However, the fundamental characteristics of the fuel cells utilizing the chemical reaction between oxygen and hydrogen obtained by reforming city gas or the like are likely to cause difficulties in changing the output power in conformity to sharp or rapid changes in power consumption. In this case, if the output power of the fuel-cell power generator is controlled in accordance with only simple or usual changes in power consumption, the generated output will be supplied with a certain delay relative to power consumption to cause deterioration in energy saving performance due to, for example, lowered utilization factor of the generated output at the initiation of power usage and surplus in the generated output at the termination of the power usage. Therefore, an adequate energy saving performance has to be assured by avoiding the response to rapid changes in power consumption and frequent startup/stop operations.
For this purpose, one conventional fuel-cell power generator is designed such that a plurality of time zones are set up according to the characteristic of changes in power consumption, and the output power of fuel cells is controlled by factors consisting of a change rate of power consumption, a dead time and an offset relative to an actual power consumption, which are defined in each of the time zones, so as to prevent the response to rapid changes in power consumption and frequent startup/stop operations (see, for example, Japanese Patent Laid-Open Publication No. 2002-291161: Patent Publication 1).
Another conventional fuel-cell power generator is designed such that power consumption is estimated in advance by simulation, the output power of fuel cells is efficiently controlled according to the estimated values (see, for example, Japanese Patent Laid-Open Publication No. 2003-61245: Patent Publication 2).
However, the above conventional fuel-cell power generators cannot be adaptively controlled in conformity to various electricity loads different in each of the homes. Specifically, in the above Patent Publication 1, it is practically difficult to calculate optimal values of the change rate, dead time and offset to be determined in advance for each of the homes, because such factors are originally varied between the homes. Moreover, it cannot cope with the situation where power consumption is largely varied due to changes in season, life style, use condition of appliances or the like.
In the above Patent Publication 2, while electricity loads are estimated by simulation in a load estimation step, such estimated values can be created only if there is previous data obtained under environmental conditions equivalent to those as the basis of the simulation. In addition, while characteristic data of fuel cells are required to perform the simulation, the characteristics of fuel cells would be varied between homes, and thereby adequate estimated values cannot be practically created. Thus, as with the generator in Patent Publication 1, it is difficult for the generator in Patent Publication 2 to estimate power consumption to be varied between homes.